In order to operate many electrically and electronically controlled motor vehicle mechanisms, actual operating states of a motor vehicle must be established so as to activate these electrically and electronically controlled mechanisms accordingly. For example, in the case of motor vehicles with braking equipment which, when the motor vehicle is in a state of standstill, automatically produces braking forces which hold the motor vehicle at a standstill, it is necessary to ascertain whether or not the vehicle is at a standstill. Examples of braking equipment of this kind are so-called electronic parking brakes (EPB) and electronic holding brakes (EFB).
As other electrical and electronic mechanisms of the motor vehicle also require information on actual operating states of the motor vehicle (e.g. travelling mode, standstill), it is usual to fall back on this information when operating the above-mentioned braking equipment. The operating state information comprises parameters which characterise the actual operating state of the vehicle. These include the speed, the acceleration, the transverse acceleration, the engine speed, the effective driving torque, the speed of one or more wheels, positions of the accelerator, brake and clutch pedals, etc.
As operating state information of this kind is generally provided by a central control of the motor vehicle, when using this information for braking equipment which is to hold the motor vehicle in a state of standstill using automatically produced braking forces, the central control and the sensors associated with the latter must also be operated when the motor vehicle is not (i.e. its ignition is not turned on). This results in an increased power consumption, which—especially where lengthy standstill periods are concerned—may cause the power supply of the motor vehicle (car battery) to discharge, so that the motor vehicle cannot be started up. Moreover, when employing this procedure, mechanisms which are controlled by the central control should not be operated while the motor vehicle is at a standstill, although the central control is in operation to control the braking equipment. Measures of this kind, which are intended to prevent additional power consumption as well as wear and damage, represent an additional expenditure.
It is also impossible in this case for the braking equipment to be controlled so as to produce braking forces when the motor vehicle is in a state of standstill if the central control, corresponding sensors connected to the latter and/or data transmission mechanisms for the braking equipment are not operating faultlessly or fail completely.
DE 36 18 532 A1, and corresponding U.S. Pat. No. 4,717,207 which is incorporated by reference herein, establishes whether a motor vehicle is at a standstill by checking whether the actual travelling speed is zero, the clutch is released, first or reverse gear is engaged and the actual angle of inclination of the motor vehicle corresponds to or is greater than a predetermined angle of inclination. If these conditions are fulfilled, the brake actuating pressure, which is predetermined at this instant by the vehicle driver by means of the brake pedal, is maintained by means of a valve which is disposed between the master brake cylinder and the wheel brake cylinders of the braking system described in this publication. The disadvantage in this case lies in the fact that no braking forces are produced without actuating the brake pedal when at a standstill if a transition to standstill has taken place without using the brake pedal. Moreover, the device described here does not enable braking forces required for standstill to be produced if the motor vehicle is not operated at all, i.e. if the ignition is turned off when at a standstill. Braking forces required for the vehicle to be at a standstill must accordingly be produced in a different way in this case, for example by actuating the hand brake or the brake pedal.
According to U.S. Pat. No. 5,820,515 a state of standstill of a motor vehicle is detected in that it is checked by using detection means whether the vehicle speed is substantially 0, whether the accelerator pedal is not actuated and whether the braking pedal is actuated. If this is the case, according to U.S. Pat. No. 5,820,515 it is established therefrom that the motor vehicle is in a state of standstill. Following this it is ascertained whether the vehicle is on an inclined road. No changes of the position of the motor vehicle are detected in this connection but merely the position in which the vehicle is in the state of standstill. A further difference with respect to the present invention results from the fact that the detection of the position in the state of standstill is not utilised to ascertain whether the vehicle is in the state of standstill. The detection of the position of the vehicle is rather performed once it has been found in the above manner that the vehicle is in the state of standstill.
According to U.S. Pat. No. 5,667,282 a detection of a state of standstill of a motor vehicle in the actual sense of the word does not take place. According to U.S. Pat. No. 5,667,282 the state of standstill of the vehicle is rather indicated in that the driver operates a parking brake switch 30. Only once the state of standstill is indicated in this manner is an inclination sensor activated establishing the inclination of the vehicle and hence the inclination of the road. Comparable to U.S. Pat. No. 5,820,515, in U.S. Pat. No. 5,667,282 as well no changes in the inclination or position of the vehicle are detected but merely the inclination in the state of standstill.